1. Field of the Invention
The present invention relates to a thin film magnetic head comprising a coil layer formed between core layers, and in particular, to a thin film magnetic head capable of appropriately suppressing magnetic saturation and improving the electrical characteristics of a conventional head even with an increase in recording current. The present invention also relates to a method of manufacturing the thin film magnetic head.
2. Description of the Related Art
FIG. 24 is a longitudinal sectional view showing the structure of a conventional thin film magnetic head. This thin film magnetic head is a recording inductive type head that is provided on the trailing-side end of a slider of a floating magnetic head, and which is opposed to a recording medium such as a hard disk or the like,
In FIG. 24, reference numeral 1 denotes a lower core layer made of a magnetic material such as a NiFe alloy or the like. Referring to FIG. 24, a gap layer 4 made of a nonmagnetic material such as Al2O3, SiO2, or the like is formed on the lower core layer 1.
As shown in FIG. 24, a coil layer 5 is spirally formed on the gap layer 4 through an insulating layer 6b made of an organic insulating material. The coil layer 5 is covered with an insulating layer 6c made of an organic insulating material.
Furthermore, an upper core layer 8 made of a magnetic material is formed, for example, by a frame plating method, on the insulating layer 6c, and extends to the portion of the gap layer 4 that is located on the side facing a recording medium.
The tip region 8a of the upper core layer 8 has a width dimension corresponding to a track width Tw in the track width direction. The base end 8c of the upper core layer 8 is connected directly to the lower core layer 1.
The conventional thin film magnetic head shown in FIG. 24 is generally inadequate for use with media having narrower tracks, and has poor overwrite performance. The term “overwrite” (OW) means overwriting, and the OW performance is evaluated by overwriting with a high frequency on the signal recorded with a low frequency, and then measuring a decrease of the residual output of the signal recorded with the low frequency from the output of the signal recorded with the low frequency before overwriting with the high frequency.
FIG. 25 is a longitudinal sectional view showing an improved example of the conventional thin film magnetic head shown in FIG. 24.
As shown in FIG. 25, a bottom pole layer 2 is formed on the lower core layer 1 to protrude in the height direction by a length L1 from the surface facing the recording medium. Referring to FIG. 25, the rear end surface 2a of the bottom core layer 2 protrudes perpendicularly (in the Z direction shown in the drawing) from the lower core layer 1. In the thin film magnetic head shown in FIG. 25, the gap depth is regulated by the length dimension L1 of the bottom pole layer 2.
Furthermore, a first insulating layer 3 is formed behind the rear end surface 2a of the bottom pole layer 2 in the height direction. The first insulating layer 3 is made of a nonmagnetic material, for example, Al2O3 (alumina), SiO2, or the like.
The upper surface of the first insulating layer 3 comprises a flat plane 3b coplanar with the upper surface of the bottom pole layer 2, and a coil forming concave plane 3a formed behind the flat plane 3b in the height direction.
A coil layer 5 is formed in a spiral pattern on the coil forming plane 3a, and coated with a second insulating layer 6 made of an organic insulating material. Furthermore, the upper core layer 8 is patterned by the frame plating method to extend from the gap layer 4 to the second insulating layer 6.
As shown in FIG. 26, the tip region 8a of the upper core layer 8 is formed with a narrow width corresponding to the track width Tw that extends from the surface facing the recording medium to a dotted line (virtual line) at the end edges 8e. The rear region 8b extending backward from the end edges 8e of the tip region 8a in the height direction is formed so that the width dimension in the track width direction (the X direction shown in the drawing) gradually increases from the track width Tw.
As described above, the first insulating layer 3 formed behind the rear end surface 2a of the bottom pole layer 2 in the height direction has the plane surface 3b coplanar with the upper surface of the bottom pole layer 2, and thus the surface on which the tip region 8a is formed is planarized, thereby facilitating high-precision patterning of the tip region 8a having a track width Tw.
The tip region 8a is exposed at the surface facing the recording medium. Furthermore, the base end 8c of the upper core layer 8 is magnetically connected to the lower core layer 1 through a lifting layer 9 made of a magnetic material. This results in the formation of a magnetic circuit from the upper core layer 8 to the lower core layer 1 through the bottom pole layer 2.
In the writing inductive head, when a recording current is supplied to the coil layer 5, a recording magnetic field is induced in the lower core layer 1 and the upper core layer 8 so that a magnetic signal is recorded on the recording medium, such as a hard disk or the like, by a leakage magnetic field from the magnetic gap between the bottom pole layer 2 magnetically connected to the lower core layer 1 and the tip portion 8a of the upper core layer 8.
The structure of the conventional thin film magnetic head shown in FIG. 25 is more suitable for use with a narrower track and has improved overwrite performance, as compared with the thin film magnetic head shown in FIG. 24.
As described above, the surface on which the tip region 8a of the upper core layer 8 is formed is planarized to cause less adverse effects, such as diffused reflection or the like, during exposure patterning of the tip region 8a by using a resist. Therefore, the tip region 8a can be easily formed with the track width Tw, and a thin film magnetic head can be manufactured capable of complying with the track narrowing that accompanies increases in recording density.
In the structure of the thin film magnetic head shown in FIG. 25, a magnetic flux flowing through the tip region 8a of the upper core layer 8 leaks less from the bottom of the tip region 8a and both end surfaces thereof in the track width direction (the X direction), thereby increasing the magnetic flux density of the tip region 8a to improve the overwrite performance.
Although, as described above, the thin film magnetic head shown in FIG. 25 is more suitable for use with a narrower track and has improved the overwrite performance, the thin film magnetic head still requires improvement in the following points.
As the recording current increases with an increase in the recording density, the magnetic flux density increases locally to easily reach magnetic saturation in the tip region 8a of the upper core layer 8, which is formed with the track width Tw, particularly in the portion near the bottom pole layer 2 at the surface facing the recording medium. Therefore, in actual writing with the thin film magnetic head, the width of magnetization reversal on a magnetization curve is increased to deteriorate the NLTS characteristic and the PW50 characteristic.
The NLTS characteristic represents a phase lead of the leakage magnetic field produced in the magnetic gap between the upper core layer 8 and the bottom pole layer 2. The phase lead is caused by a nonlinear distortion due to the influence of a leakage magnetic field leaking from a magnetic recorded signal recorded on the recording medium toward the head.
The PW50 characteristic represents a measured half width of the reproduced wavelength. The smaller the half width, the more the recording resolution is improved.
In order to solve the above problem, the length dimension L1 of the bottom pole layer 2 in the height direction can be increased. However, the length dimension L1 is a dimension for controlling the gap depth Gd, and thus a change in the length dimension L1 causes changes in various electric properties. Therefore, the ability to change the length dimension L1 is limited.
The problem of magnetic saturation can also be solved by increasing the length dimension L2 of the tip region 8a of the upper core layer 8 in the height direction.
However, lengthening the tip region 8a of the upper core layer 8 deteriorates the overwrite performance, and causes the need to form the tip region 8a, not only on the plane surface 3b formed in the first insulating layer 3, but also on the rising second insulating layer 6.
Therefore, the tip region 8a cannot be formed only on the plane surface 3b, which causes difficulties in forming the tip region 8a with high pattering precision due to the problem of diffused reflection in exposure of the resist.
Also, the tip region 8a of the upper core layer 8 reaches magnetic saturation as described above, and thus a magnetic flux leaks from the surface facing the recording medium in a range wider than the track width Tw to cause the problem of increasing the amount of side fringing.